Process for the preparation of a hydrogen-rich stream

ABSTRACT

A process for the preparation of a hydrogen-rich stream comprising contacting a carbon monoxide-containing gas, methanol and water in at least one shift step in the presence of a catalyst comprising copper, zinc and aluminium and/or chromium at a shift inlet temperature of at least 280° C. and a pressure of at least 2.0 MPa.

The invention relates to a process for the preparation of ahydrogen-rich stream and provides a facile process for boosting capacityof fuel-based hydrogen plants.

Hydrogen plants can utilise fuels such as natural gas, liquidhydrocarbons or solid fuels like coal or biomass. In these plants,hydrogen production takes place in four consecutive procedures—feedpurification followed by steam reforming (or gasification), water gasshift (WGS) and purification. These procedures are further described inKirk-Othmer and Ullman.

The WGS reaction is described in the following equation:CO+H₂O→CO₂+H₂  (1)

It is a slightly exothermic reaction used for producing more hydrogen.Known WGS catalysts in industrial high temperature shift (HTS)applications are high-temperature catalysts that are chromium-supportedand iron-based, and they are sometimes promoted with copper. Theoperational range for the HTS is typically 340-360° C. inlet temperatureand with exit temperatures that are approximately 100° C. higher. Theoperational range of the inlet temperature for low temperature shift(LTS) catalysts is from 200° C. (or 20° C. above the dew point of thegas). The inlet temperature should be kept as low as possible Furtherdetails on catalysts for shift reactions and operating temperature aregiven in Catalyst Handbook, 2. Ed. Manson Publishing Ltd. England 1996.

In addition to these catalysts, Haldor Topsøe A/S has marketed amedium-temperature shift catalyst that is Cu-based and capable ofoperating at temperatures up to 310° C. Various vendors offersulphur-tolerant catalysts for the gasification-based plants. However,these plants are not widely used for hydrogen production.

Methanol is produced on a large scale of more than 30 MM t/y. Basically,methanol is produced in very large plants with capacities of more than2000 MTPD at places where natural gas is cheap. The production cost formethanol at places with cheap natural gas is estimated to be in theorder of 60-80 USD/MT.

In the future, it is expected that methanol can be available in largequantities and to a price that on an energy basis might be significantlylower than the oil price.

In recent years there have been numerous studies of steam reforming ofmethanol for producing hydrogen and in particular hydrogen for fuelcells. The disadvantage of the steam reforming process is that the heatof reaction has to be supplied through a wall and the equipment as suchbecomes cumbersome.

Catalysts for low temperature steam reforming of methanol are copperbased or optionally based upon noble metals. Some companies, forinstance Haldor Topsøe A/S, offer commercial products.

U.S. Pat. No. 5,221,524 describes a hydrogen production process where areformed gas is cooled before undergoing a low temperature shiftreaction catalysed by a copper catalyst with an inlet temperature of205° C. Liquid methanol is dispersively supplied to the shift converterand unconverted methanol is recycled to the methanol supply source andthe shift reactor. The catalyst has activity both for low temperatureshift conversion of carbon monoxide and the steam reforming reaction ofmethanol to hydrogen and carbon dioxide. The heat generated from theshift conversion reaction is utilised to accelerate the endothermicreaction for methanol decomposition.

U.S. Patent Application No. 2001/0038816 describes a gas generator forgenerating hydrogen utilising a shift reactor supplied with a reformedgas and water containing small amounts of methanol for frost protection.The gas generator is connected to a fuel cell set-up.

JP Patent Application No. 59203702 describes a hydrogen manufacturingprocess whereby methanol and steam are reacted in a shift reactor andthe effluent gas is purified and hydrogen is removed. The remaininggases are combusted and the heat generated is used as a heat source forthe methanol decomposition in the shift reactor.

JP Patent Application No. 3254071 describes a process for modifyingalcohol and generating hydrogen for a fuel cell. Natural gas is reactedwith air in a methanol modifier, and the heat generated is used forconversion of the methanol/water mixture.

It is an objective of the invention to provide a process for productionof hydrogen by utilising a catalyst capable of operating at a wide rangeof temperatures.

According to the invention, there is provided a process for thepreparation of a hydrogen-rich stream comprising contacting a carbonmonoxide-containing gas, methanol and water in at least one shift stepin the presence of a catalyst comprising copper, zinc and aluminiumand/or chromium.

The process can be carried out by adding methanol to the feed stream toa water gas shift reactor containing a Cu-based catalyst comprisingzinc, aluminium and/or chromium and resulting in a catalyticdecomposition of the methanol along with the water gas shift reaction.In the isothermal case, the heat released by the exothermic Water GasShift Reaction balances the heat used for the endothermic steamreforming of methanol. The sensible heat in the feed streams may furtherbe used in the process whereby a significant larger amount of methanolmay be steam reformed.

The catalyst used in the process of the invention is capable ofoperating both at lower temperatures and at temperatures above 350° C.

By using this catalyst in the process the hydrogen production from theunit may be boosted up to 100%. Alternatively, the process can be usedto decrease the load on the reforming section. A capacity increase ofammonia plants is also provided by applying the process of the inventionin such a plant.

The endothermic methanol steam reforming reaction:CH₃OH+H₂O→3H₂+CO₂  (2)obtains the necessary heat of reaction from the sensible heat in the gasas well as from the latent heat from the WGS reaction. The catalystutilised in the process of the invention tolerates the maximum inlettemperature and is still active at a much lower temperature primarilydetermined by the desire to keep the outlet methanol concentration aslow as possible (typically in the temperature range from 240-320° C.).

Experiments with addition of methanol to iron-based shift catalyst haveshown that a significant amount of methane formation takes place onthese catalysts. This is also the result of the large scale productionof town gas using the Hytanol process developed by Lurgi.

The invention is applicable to a hydrogen plant on any scale. Inaddition the invention proves to be particularly useful for peak shavingpurposes in gasification based combined cycle power plant or in fuelprocessors, e.g. by injecting a (liquid) methanol water mixture afterthe autothermal reformer.

The FIGURE illustrates the process of the invention. Synthesis gas 1 isinjected into a shift section 2. A stream of methanol 3 and water 4 arealso injected into the shift section 2 where the shift step occurs. Themethanol stream 3 can be added either in liquid form or in vapour form.The water 4 can be added as vapour. The shift section contains catalysthaving activity both for the shift conversion reaction of the carbonmonoxide and the steam reforming reaction of methanol. The heat requiredfor the endothermic steam reforming reaction of methanol is provided bythe heat obtained in the shift conversion reaction. The product is ahydrogen-rich stream 5.

The catalysts suitable for the process contains copper, zinc, aluminiumand/or chromium. Using this catalyst results in an increase in capacityand the catalyst is active at both lower temperatures and attemperatures above 350° C.

Addition of methanol and water in vapour form has the advantage thatcomplicated dispersive elements required to distribute liquid methanolin the shift section are avoided. An additional benefit is the highreactant partial pressure created throughout the shift section. Methanolcan be added as a single stream, which is an advantage.

The shift section can comprise a single shift step or a combination ofshift steps. An embodiment of the invention comprises a process where atleast one shift step is a medium-temperature or a high temperature shiftstep. Another embodiment of the invention comprises a process where themedium or high temperature shift step is followed by a low temperatureshift step. Other combinations of shift steps are also possible and areencompassed by the process of the invention.

The synthesis gas stream 1 can be obtained from various sources forexample a steam reformed gas, a secondary reformer, an autothermalreformer or an upstream pre-reformer.

A particular embodiment of the invention comprises the process where ahydrocarbon stream and steam are first pre-reformed to obtain methaneand then steam reformed to obtain a gas containing carbon monoxide,before entering the shift step. After the shift reaction the hydrogenproduced is separated and unconverted methanol is recycled to thepre-reformer.

Besides methanol, other similar species like methyl format, formaldehydeor formic acid may be used.

The advantages of the process of the invention are illustrated in thefollowing examples.

EXAMPLES

The following catalysts from Haldor Topsøe A/S have been used in theexamples:

-   Catalyst A: SK201-2—a high-temperature shift catalyst comprising    oxides of copper, iron and chromium.-   Catalyst B: MK101—methanol synthesis catalysts comprising oxides of    copper, zinc and aluminium.-   Catalyst C: MK121—methanol synthesis catalysts comprising oxides of    copper, zinc and aluminium.

Example 1 is a comparative example, which serves to demonstrate thatcatalysts such as catalyst A are not suited for the production ofhydrogen from methanol cracking. Examples 2-13 serve to demonstrate thescope of the present invention using copper-based catalysts. In theseexamples, it is demonstrated how hydrogen production, according to theprocess of the invention, may be improved significantly and withextremely high efficiency. Examples 14-18 are comparative examplesdemonstrating the performance of the catalysts under normal water gasshift conditions. Catalyst C is used in these examples.

Example 1 Comparative

10 g of catalyst A is activated by means of steam and a dry gascontaining 15% CO, 10% CO₂ and 75% H₂. It is further tested at 380° C.at a dry gas flow of 50 Nl/h and a steam flow of 45 Nl/h at a pressureof 2.3 Mpa. After 70 hours the CO concentration in the dry exit gas is3.7%. Further addition of 0.5 Nl/h of methanol causes the CO exitconcentration to increase to 4.0% and the exit CH₄ concentration toincrease from 20 ppm to 1000 ppm. Furthermore, the water condensed afterthe reactor contained a significant amount of unconverted methanolcorresponding to approximately 50% of the methanol added. When themethanol was removed the CH₄ formation decreased to 25 ppm and the COformation to 3.9%.

The result clearly shows that this catalyst is unsuitable for catalyticmethanol decomposition into hydrogen and carbon oxides.

Example 2

15.2 g of catalyst B is reduced in diluted hydrogen (1-5 vol %) at 185°C. at a pressure of 0.1 MPa, and the synthesis gas being comprised of43.1% hydrogen, 14.3% carbon monoxide, 11.1% carbon dioxide and 31.5%nitrogen is introduced. The pressure is increased to 2.5 MPa and thetemperature is raised to 235° C. A solution of 19.63% wt/wt methanol inwater is evaporated and co-fed with the synthesis gas. The dry gas flowis 100 Nl/h, whereas the liquid flow is 41.6 g/h corresponding to asteam flow of 41.6 Nl/h and a methanol flow of 5.7 Nl/h. The exit gas isanalysed after condensation of residual steam and methanol. At theseconditions the CO exit concentration amounts to 0.90% and the CO₂ exitconcentration is 21.7% and the dry flow gas flow is increased to 130Nl/h. No CH₄ is observed at any time the detection limit beingapproximately 1 ppm.

At these conditions, the exit temperature is measured to be 242° C.immediately after the catalyst bed and the liquid flow exit in thereactor is 20.8 g/h with a methanol concentration of 8.14% wt/wt. Themethanol exit flow is thus 1.18 Nl/h. This corresponds to a methanolconversion C(M):C(M)=(methanol flow_(inlet)−methanol flow_(exit))/methanolflow_(exit))/methanol flow inlet*100%=79.3%.

The carbon monoxide conversion is calculated as C(CO):C(CO)=(CO flow_(inlet)−CO flow_(exit))/CO flow inlet*100%=91.8%.

The productivity of hydrogen is calculated as Prod(H2):Prod(H2)=(hydrogen flow_(exit)−hydrogen flow_(inlet))/mass ofcatalyst=1700 Nl H2/kg/h.

Carbon mass balance, C(in)/C(ex), is found to be 1.02. The results aresummarized in Table 1.

Examples 3-7

As Example 2 except for variations in temperature, dry gas flow andliquid flow as according to Table 1. The catalyst is the same batch asused in Example 2. Analysis of the condensable part of the exit gas ofExample 7 reveals a concentration of ethanol of 10 ppm wt/wt. No higheralcohols, methane or any other hydrocarbons are observed in any ofExamples 3-7. The selectivity of methanol conversion to carbon oxidesand hydrogen is thus 100% within the accuracy of the experiments.

Example 8

15.1 g of catalyst C is reduced in dry diluted hydrogen (1-5 vol %) at185° C. at a pressure of 0.1 MPa and the synthesis gas being comprisedof 43.1% hydrogen, 14.3% carbon monoxide, 11.1% carbon dioxide and 31.5%nitrogen is introduced. The pressure is increased to 2.5 MPa and thetemperature is raised to 216° C. A solution of 22.37% wt/wt methanol inwater is evaporated and co-fed with the synthesis gas. The dry gas flowis 50 Nl/h, whereas the liquid flow is 16.0 g/h corresponding to a steamflow of 15.5 Nl/h and a methanol flow of 2.5 Nl/h. The exit gas isanalysed after condensation of residual steam and methanol. At theseconditions the CO exit concentration amounts to 0.64% and the CO₂ exitconcentration is 22.3% and the dry flow gas flow is increased to 63Nl/h. No CH₄ is observed at any time, the detection limit beingapproximately 1 ppm. At these conditions, the exit temperature ismeasured to be 219° C. immediately after the catalyst bed and the liquidflow exit the reactor is 18.7 g/h with a methanol concentration of11.26% wt/wt. The methanol exit flow is thus 1.47 Nl/h.

The conversions are calculated as above with C(M)=56.9% and C(CO)=94.3%.The productivity of hydrogen is Prod(H2)=749 Nl H2/g/h. Carbon massbalance is found to be 1.00. The results of methanol-boosted shift overcatalyst C are summarized in Table 2.

TABLE 1 Example 2 3 4 5 6 7 inlet Temp 235 235 273 273 311 312 (° C.)exit Temp 242 237 275 275 312 309 (° C.) Inlet dry flow 100 50 100 50100 100 (N1/h) inlet liquid 41.6 18.8 41.7 17.8 41.5 60.0 flow (g/h)inlet steam 42 19 42 18 42 60 flow (N1/h) inlet MeOH 5.7 2.6 5.7 2.4 5.78.2 flow (N1/h) exit dry flow 130 66 137 67 137 148 (N1/h) exit liquid20.8 7.9 19.5 9.4 17.0 27.6 flow (g/h) [MeOH]_(exit) 8.14 8.26 3.58 2.031.03 1.27 (% wt/wt) [CO]_(exit) (mole 0.90 0.66 1.20 1.30 1.79 1.20 %)C(M) (%) 79.3 82.3 91.5 94.6 97.8 97.0 C(CO) (%) 91.8 93.8 88.4 87.782.7 87.5 Prod(H₂) 1700 940 2080 970 2090 2640 (N1/kg/h)C_((in))/C_((ex)) 1.02 0.99 0.98 0.98 0.98 0.98

Example 9

This experiment is similar to Example 8 except for variation in dry gasflow and liquid flow as shown in Table 2. The selectivity of methanolconversion to carbon oxides and hydrogen is 100%.

Example 10

The catalyst used in Examples 8-9 is left on stream for 120 hours at aninlet temperature of 313° C., a dry gas flow of 100 Nl/h, a liquid flowof 60 g/h, a pressure of 2.5 MPa and with feed compositions as inExamples 8-9. The selectivity of methanol conversion to carbon oxidesand hydrogen is 100%. The exit concentration of carbon monoxide isconstant at 1.25±0.05% in this period. After the 120 hours period thecondensate was analysed again with the results given in Table 2.

Examples 11-13

These experiments are similar to Example 10 except for variations intemperature, dry gas flow and liquid flow as shown in Table 2.

Examples 14-17 Comparative

These experiments are similar to Examples 10-13 except that methanol isexcluded from the liquid feed. The results catalyst C without methanoladdition are shown in Table 3.

TABLE 2 Example 8 9 10 11 12 13 Inlet Temp 216 216 313 313 275 236 (°C.) Exit Temp. 219 224 310 314 279 244 (° C.) Inlet dry flow 50 100 100100 100 100 (N1/h) Inlet liquid 18.7 60 60 41.9 39.8 41.7 flow (g/h)Inlet steam 18 58 58 40 38 40 flow (N1/h) Inlet MeOH 2.9 9.4 9.4 6.6 6.26.5 flow (N1/h) Exit dry flow 63 131 148 139 139 134 (N1/h) Exit liquidflow 16.0 39.6 31.9 20.3 19.3 21.4 (g/h) [MeOH]_(exit) 11.26 14.77 1.521.29 3.45 10.87 (% wt/w) [CO]_(exit) 0.64 0.95 1.23 1.86 1.34 1.11 (mole%) C(M) (%) 56.9 56.4 96.4 97.2 92.5 75.1 C(CO) (%) 94.3 91.2 87.2 81.886.9 89.5 Prod(H2) 750 1700 2550 2140 2180 1920 (N1/kg/h)C_((in))/C_((ex)) 1.00 1.03 1.04 1.02 1.01 1.03

TABLE 3 Example No. 14 15 16 17 Inlet Temp. (° C.) 236 274 312 313 ExitTemp. (° C.) 253 289 325 327 Inlet dry flow (N1/h) 100 100 100 100 Inletliquid flow (g/h) 31.8 31.8 31.8 46.2 Inlet steam flow (N1/h) 40 40 4057 Inlet MeOH flow (N1/h) 0 0 0 0 Exit dry flow (N1/h) 116 116 115 116Exit liquid flow (N1/h) — — — — [MeOH] exit (% wt/wt) — — — — [CO] exit(mole %) 0.88 1.13 1.62 1.15 C(M) (%) — — — — C(CO) (%) 92.9 90.8 87.090.8 Prod (H2) (N1/kg/h) 1060 1040 1000 1040 C(in)/C(ex) 1.03 1.03 1.031.03

The above examples clearly demonstrate that hydrogen production may besignificantly improved by addition of methanol to a synthesis gas andexposing the resulting mixture to a catalyst containing copper. Thus,when 15 g of the catalyst MK121 is exposed to synthesis gas at an inlettemperature of 313° C. at a dry gas flow of 100 Nl/h, a steam flow of 57Nl/h and 25 bar pressure, the hydrogen production amounts to 1040Nl/kg/h (Example 17). In this example the exit temperature is 327° C.and the CO concentration is 1.15%. With the same catalyst, addition of9.4 Nl/h methanol to the feed but otherwise the same conditions ofoperation, the hydrogen productivity increases to 2550 Nl/kg/h (Example10). In this example the exit temperature is 310° C. and the COconcentration is 1.23%.

1. A process for the preparation of a hydrogen-rich stream comprisingreforming a hydrocarbon feed to obtain a carbon monoxide-containing gas,and contacting the carbon monoxide-containing gas, methanol and water inat least one shift step without external addition of heat in thepresence of a catalyst comprising copper, zinc and aluminum and/orchromium, at a shift inlet temperature of at least 280° C. and apressure of at least 2.0 MPa.
 2. A process according to claim 1, whereinthe methanol and water are in vapour form.
 3. A process according toclaim 1, wherein the methanol and water are in liquid form.
 4. A processaccording to claim 1, wherein the at least one shift step is a MediumTemperature or High Temperature shift step.
 5. A process according toclaim 4, wherein the Medium Temperature or High Temperature shift stepis followed by a Low Temperature shift step.
 6. Process according toclaim 1, wherein the hydrocarbon feed is pre-reformed before thereforming step.
 7. Process according to claim 6, wherein unreactedmethanol is separated from the shift step effluent and re-cycled to thepre-reforming step.
 8. Process according to claim 4, wherein the shiftinlet temperature is at least 300° C.